The present invention relates to an apparatus for inflating a vehicle occupant protection device and particularly relates to an electrically actuatable pyrotechnic igniter for an air bag inflator.
An inflatable vehicle occupant protection device, such as an air bag, is inflated in the event of sudden vehicle deceleration such as occurs in a vehicle collision. The air bag restrains movement of a vehicle occupant during a vehicle collision. The air bag is inflated by inflation fluid from an inflator. The inflation fluid may be stored gas which is released from the inflator and/or gas generated by ignition of combustible gas generating material in the inflator. The inflator uses an electrically actuatable pyrotechnic igniter to open the container and release the stored gas and/or to ignite the gas generating material.
The electrically actuatable pyrotechnic igniter contains a charge of ignition material. The pyrotechnic igniter also contains a bridgewire that is supported in a heat transferring relationship with the ignition material. When the pyrotechnic igniter is actuated, an actuating level of electric current is directed through the bridgewire in the igniter. This causes the bridgewire to become resistively heated sufficiently to ignite the ignition material. The ignition material then produces combustion products that open the container and release the stored gas and/or ignite the gas generating material.
Radio frequency interference (RFI) suppression filters are commonly incorporated in an electrically actuatable pyrotechnic igniter. RFI suppression filters ensure that unwanted radio frequency (RF) signals are suppressed and allow the passage of direct current and low frequency alternating current. Failure to suppress RF signals might lead to the undesired actuation of the igniter.
In many cases, electrically actuatable pyrotechnic devices incorporating these RFI filters are also required to provide a gas-tight seal to protect sensitive components or materials contained within an enclosure. Many electrically actuatable pyrotechnic igniters incorporate a hermetically sealed chamber for their ignitable material that is vulnerable to degradation by the intrusion of water vapor.
The present invention is a pyrotechnic device. The pyrotechnic device comprises a body of ignitable material. A pair of electrodes provide electrical energy to heat and ignite the body of pyrotechnic material. The electrodes extend through an electrical insulation housing. The electrical insulation housing has surfaces defining a chamber through which the electrodes pass. A body of a solid electromagnetically lossy, substantially gas impermeable material is positioned within the chamber. The lossy material comprises a vitreous ceramic matrix consisting essentially of about 5% to about 50% by weight of a multi-component glass binder and about 50% to about 95% by weight of an electromagnetically lossy ferromagnetic and/or ferroelectric filler. The body of lossy material is fused to the surfaces defining the chamber in the electrical insulation housing and to the electrodes.